A modified & epsilon;-NTU analytical model for the investigation of counter-flow Maisotsenko-based cooling systems

In this work the e-NTU method has been adapted for the application of a countercurrent evaporative heat exchanger featuring a complex heat transfer surface. The study highlights some challenges related to extending analytical models that were validated on simple geometries and proposes the calibration of the e-NTU method by experimentally measuring the overall heat transfer coefficient (UA) of the heat exchanger. Through a laboratory prototype of the M-cycle, two different operating conditions were investigated (mild and hot-dry climates) which reported almost constant UA values of 14.8 W/K and 16.1 W/K respectively. The obtained results from the model prediction were compared with the experimental data obtaining average errors on the outlet temperatures and on the cooling capacity lower than 1.5% in the case of simulation of hot and dry climate. The positive results allowed to extend the calculation to operating conditions not tested experimentally, highlighting how it is necessary to have NTU over 2-2.5, while the recirculation rate must be kept below 0.4 to make efficient use of the water. The aim is to support the implementation of the technology in full-scale applications, where the M-cycle is used alone or to complement a vapor compression system.